Research which led to the development of the 3Phase fertiliser program was started in response to the need to phase out poultry manure because of community concerns with its use. Although a useful soil amendment and source of nutrients, poultry manure stockpiles provide a breeding ground for stable flies and create odour problems.
The 3Phase program presented here is based on eight years of fertiliser research on Iceberg lettuce grown on the sandy soils of the Swan Coastal Plain with sprinkler irrigation. This schedule gave the highest yields and best quality throughout the year, while being practical to apply and economical with labour.
The program is also suitable for Cos lettuce, with small changes to timings, and has been successfully adapted by growers for other leafy and heading lettuce.
Boomspray applications recommended in Phase 1 however are not suitable for use on some soft-leaved types such as Green Festival and Buttercrunch.
The sandy soils of the coastal plain provide a free-draining, easily worked growing medium. Nutrients are freely available in the soil solution for plant uptake. Some nutrients are highly mobile and easily lost through leaching.
Nitrate-nitrogen is particularly susceptible to leaching and is a major groundwater pollution concern. Pay careful attention to fertiliser application to:
- maximise the efficiency of fertiliser use
- minimise loss through leaching
- maximise return on the dollars spent on fertiliser.
The program outlined here is based on research conducted on some of the most infertile soils in the region. It developed cost-effective strategies for maximising yield in a ‘worst case’ situation.
Fertiliser and cost savings are achieved in the 3Phase program by making informed choices about fertiliser type, application rates, methods and timing — matching application to crop demand. To achieve this, the life of the crop is considered in three phases: establishment, rapid growth and maturation (see Figure 1).
Different fertiliser strategies are used to optimise growth in each of these phases.